Design of the Capsule (13M-01K) for Irradiation of Fuel Cladding Materials in HANARO

Nuclear-grade zirconium alloys contain more than 95% Zr, and therefore most of their properties are similar to those of pure zirconium. ZIRLO material, used in fuel rod cladding, structural and flow mixing grids, instrumentation tubes, and guide thimbles, increases margin-to-fuel-rod-corrosion limits and enhances fuel assembly structural stability. The demonstrated corrosion resistance and enhanced structural stability of ZIRLO cladding enable longer cycle lengths at higher temperatures without reducing operating margins. An instrumented capsule (13M-01K) was designed and fabricated for evaluation of the neutron irradiation properties of Zirlo material, which is commonly used for cladding of nuclear fuel. This capsule is now being irradiated for 2 cycles at CT test hole of HANARO, which was started at Jan 27 and will be ended at Mar 31, 2014. The structure of the capsule was based on the previous capsule (11M-22K capsule) which was successfully irradiated at the same hole of HANARO. In the capsule, 182 specimens such as tensile specimens of plate type and ring type specimens were placed. Most of them are made of Zirlo, but a few are HANA material that is developed in KAERI. The irradiation test was requested by 4 universities including Dong-Kook and Han-Yang etc. The capsule is composed of 5 layers, each of which had Al holder containing several specimens and an independent electric heater, thermocouples etc. During the irradiation test, temperatures of the specimens and fast neutron fluence were measured by 14 thermocouples and 5 sets of Ni-Ti-Fe neutron fluence monitors installed in the capsule. The capsule is irradiated for 2 cycles (28 days) at the CT test hole of HANARO of a 30MW thermal output at 350-390 .deg. C up to a fast neutron fluence of 9.6Χ10²⁰ (n/cm²) (E>1.0 Mev). In this capsule, the two kinds of irradiation tests are performed at quite different temperatures. At upper 3 layers of the capsule, specimens for irradiation at high-temperature are inserted, and they would reach higher than 950 .deg. C during irradiation. The high temperature irradiation test in necessary for development of materials to be used materials for VHTR among future reactor systems